1. Field of the Invention
The present invention relates to furnaces for use in heat treatment or the like, such as heat-treat furnaces, heating furnaces, etc., and more particularly, relates to furnaces of this kind in which works to be treated can be efficiently carried into and out of a furnace chamber without being affected by the shape of the works.
2. Description of the Prior Art
Conventionally, three types of furnaces, that is, a convection type, a radiation type, and a conduction type, have been employed, and it has been considered that among these three types, the convection type is a preferred one to treat works at an appropriate temperature. In the convection type of furnace, however, it is difficult to uniformly control the temperature within the furnace because the furnace is arranged such that a burnt gas produced by a burner or the like is blown into the furnace and forcedly convected within the furnace only by the blowing pressure. Consequently, variations easily occur in quality of the treated works, and, on the other hand, there is a limitation in improving the furnace efficiency from the viewpoint of the furnace structure per se.
To overcome the above-mentioned problem, there has been proposed a furnace which comprises a work mounting turntable provided rotatably, and a circulating fan provided coaxially with the turntable to thereby forcedly circulate heated gases within a furnace chamber; as disclosed in Japanese Patent Unexamined Publication No. 59-38322 assigned to the same Assignee as the present application.
The proposed furnace will be described hereunder by reference to FIGS. 8 through 11. A furnace chamber 1 is surrounded by an upper and a lower fireproof member 2 at upper, lower and side portions thereof, and is provided at the upper portion thereof with a gas burner 3 as heating means facing to the furnace chamber 1. On the side portions of the furnace chamber 1, a work inlet 4 and a work outlet 5 are provided so as to be in close vicinity to each other. Within the furnace chamber 1, a work mount turntable 6 is provided so as to be rotatable about the vertical axis thereof and a circulating fan 7 constituted by a sirocco fan or the like is provided coaxially with the turntable 6 so as to turn about the same axis above the center portion of the turntable 6. In this case, a plurality of partition plates 8 are uprightly provided on the outer circumference of the upper surface of the turntable 6 to form a plurality of work mount portions 9 at suitable intervals. In this furnace, the work mount portions 9 are arranged in two stages, and a plurality of diffusing blades 10 are formed at the inside of and coaxially with the circular arrangement of the work mount portions 9 so as to face the circulating fan 7. A rotary shaft 11 of the turntable 6 is vertically supported at the center of a frame 12 supporting the furnace chamber 1 through the lower fireproof member 2. A driven gear 13 attached to the lower end of the rotary shaft 11 engages with a drive gear 15 attached to a rotary shaft 14a of an electric motor 14 disposed within the frame 12 for driving the turntable, so that the rotation of the motor 14 acting as driving means is transmitted to the turntable 6 so as to cause the turntable 6 to rotate intermittently or continuously.
On the other hand, a rotary shaft 16 supporting the circulating fan 7 passes through the upper fireproof member 2 to project upward. A transmission belt 21 is entrained about a driven pulley 17 attached to the upper end of the rotary shaft 16 and a drive pulley 20 attached to a shaft 19a of a circulating fan driving electric motor 19 disposed on the upper face of the upper fireproof member 2 of the furnace chamber 1 through a support member 18. The rotation of the motor 19 is transmitted to the circulating fan 7 by the pulleys 17 and 20 and the transmission belt 21. In this case, the circulating fan 7 is made to rotate at a speed higher than the turntable 6.
In the thus arranged furnace, it is desired that carrying-in of works A from the work inlet 4 and carrying-out of the same from the work outlet 5 can be performed continuously. Therefore, as shown in FIG. 10, the work inlet 4 is formed to downward incline toward the turntable 6 and an inclined portion 23 for temporarily mounting a work is formed to be connected to the work inlet 4 through an openable/closable cover 22 provided at the outer side of the work inlet 4. Moreover, at the outside of the work temporarily mounting portion 23, there is provided a swingable work supply portion 24 which is adapted to be shortened at its free end to the work temporarily mounting portion 23 by suitable operation means (not shown) so that one work A is made to stand by at the outside of the furnace chamber 1 and then made to come onto a certain one of the work mount portions 9 of the turntable 6 through the work inlet 4 by opening the cover 22. At the work outlet 5, there is provided a hook-like work carry-out bar 25 for drawing a work A out of the furnace chamber 1 in synchronism with the rotation of the turntable 6, the bar 25 adapted to be shuttled by not-shown driving means. The work outlet 5 is formed to be inclined downward outward so that a work A may be smoothly carried out to a shooter 26. Alternatively, the work carry-out bar 25 may be arranged, as shown in FIG. 11, so as to be constituted by a bar body 25a, an end support 25b, an inner support 25c, and a movable rod 25d, the supports 25b and 25c being formed to oppose to each other at the end of the bar body 25a and at a somewhat inner position therefrom, respectively, the movable rod 25a being formed so as to pass through the inner wall 25c movably to shuttle relative to the top wall 25b, thereby making it possible that a work A is held between the movable rod 25d and the end support 25b, carried out of the furnace chamber, and then released from the held state.
In the thus arranged furnace, it is possible that the air blast from the circulating fan 7 is diffused by the diffusing blades 10 so that the surface of the respective work A is heated uniformly. There is a further effect that it is possible to perform the heat treatment of the works A at a high speed in cooperation with the rotation of the turntable 6. In the thus arranged furnace, however, there remain some unsolved problems as to the way how to carry the works A into and out of the furnace. In the example as shown FIG. 10, a work A is made to slide or roll down by the use of inclination of the work inlet 4 so as to be mounted onto the turntable 6 from the work temporarily mounting portion 23. At the work outlet 5 there is provided the hook-like work carry-out bar 25 for drawing a work A out of the furnace chamber 1 into the downward inclined work outlet 5 from which the work A is made to slide or roll down to be carried out from the furnace. In the alternative example as shown in FIG. 11, a work A is slided while being held between the end of the movable rod 25d and the end support 25b.
Such a work carry-in/out system by the use of gravity and inclination of the work inlet and outlet 4 and 5 and such a system in which a work A is fallen down after carried out while being held by the work carry-out bar 25, are suitable only for works A having a shape capable of rolling easily. In the sliding carry-in system, it is necessary that the work A is finished up to have a smooth surface in some degree and there is a risk that a work A having a complex surface is injured when it is slided down. Moreover, in the system employing the work carry-out bar 25, the works are limited to those having a shape capable of being held easily and it is therefore difficult to use the system for the works A having an external shape complex or apt to be injured.